This invention relates to ultrasonic characterization of tissue and particularly to characterization of the mechanical properties of tissue during treatment thereof with therapeutic ultrasound. In a paper entitled xe2x80x9cSonoelasticity Images Derived from Ultrasound Signals in Mechanically Vibrated Tissues,xe2x80x9d by R. M. Lerner, S. R. Huang and K. J. Parker published in Ultrasound Medical Biology, vol. 16, pp. 231-239, 1990 there is described a technique for measuring the mechanical properties of tissue by inducing mechanical vibrations therein and measuring ultrasonic echos from within the tissues during vibration thereof. Such procedures can sense the effective stiffness of tissue constituents and produce cross-sectional images depicting induced displacement or strain.
In U.S. Pat. No. 4,484,569, which is assigned to the assignee of the present invention, there is described a combined transducer for providing diagnostic imaging using ultrasound, and for providing therapeutic application of high intensity focused ultrasound for treatment of tissue by producing lesions therein.
In a paper entitled xe2x80x9cElastography Imaging of Thermal Lesions in Soft Tissue: A Preliminary Study In Vitroxe2x80x9d in Ultrasound Medical Biology, vol. 24, pp. 1449-1458 (1998) Stafford et al. have shown that internal thermal lesions induced by high intensity focused ultrasound could perturb the elastic moduli of normal tissue and produce ultrasonically detectable changes in displacement, measured after the treated tissue was imbedded in a gel block. These studies used a large paddle to mechanically induce external displacement of the tissue.
It is an object of the present invention to provide a new and improved method for measuring the mechanical properties of tissue using ultrasound, and in particular a method for providing measurement of induced lesions in tissue during therapeutic application of high intensity focused ultrasound thereto.
In accordance with the invention there is provided a method for evaluating tissue characteristics, which includes operating an ultrasonic therapeutic transducer to insonify a region of tissue and cause induced tissue displacement. An ultrasonic diagnostic transducer is operated to observe the tissue displacement and thereby evaluate the mechanical characteristics of the tissue.
According to a preferred method the therapeutic transducer insonifies the tissue along a radiation axis and the diagnostic transducer transmits and receives ultrasonic signals along the same radiation axis. Preferably the ultrasonic therapeutic transducer is operated during a first selected time interval and the ultrasonic diagnostic transducer is operated during a second selected time interval immediately following the first selected time interval.
According to the invention there is provided a method for ultrasonic treatment of tissue including locating a tissue region to be treated using diagnostic ultrasound, radiating the tissue region using high power therapeutic ultrasound radiation and observing mechanical characteristics in the tissue region using the diagnostic ultrasound to evaluate effectiveness of the therapeutic ultrasound radiation.
In a preferred method of treatment, locating the tissue region is done by observing baseline mechanical characteristics of the tissue region. In addition there may be provided a reduced energy stimulus pulse of the therapeutic ultrasound radiation to irradiate the tissue during a first selected time interval. Mechanical characteristics of the tissue are observed during a second selected time interval immediately following the first time interval using diagnostic ultrasound thereby to observe baseline characteristics of the tissue region. After ultrasonic treatment of the tissue the tissue characteristics can be observed by irradiating the tissue with a reduced energy stimulus pulse of the therapeutic ultrasound radiation and thereafter observing mechanical characteristics of the tissue region using diagnostic ultrasound. In practicing the treatment method of the invention the location of the focal volume of the therapeutic ultrasound radiation within tissue may be determined. A reduced energy pulse of therapeutic ultrasound radiation may be supplied to the tissue during a first selected time interval and the mechanical response of the tissue region to be treated will be observed during a second selected time interval immediately following the first selected time interval using the diagnostic ultrasound to thereby locate the focal volume of the therapeutic radiation in the tissue.
For a better understanding of the present invention, together with other and further objects, reference is made to the following description, taken in conjunction with the accompanying drawings, and its scope will be pointed out in the appended claims.